This invention relates generally to audio signal processing and more specifically concerns audio signal processing which simulates analog tape saturation.
Until recent years, all popular forms of music have been recorded by analog means to magnetic tape. However, the advent of digital technology has revolutionized the industry by providing a much more powerful and precise means of recording. Therefore, an increasing amount of material is now recorded digitally.
While this drastic change in technology provides many advantages over the previous method, digital technology has not been well received among many critical listeners. This is primarily due to the difference in nature of these recording processes. The analog recording process has a very limited dynamic range, typically on the order of 60 dB. Therefore, it has been desirable to record signals as "hot" or high in level as possible in order to obtain the best signal-to-noise ratio. The hotter a signal is recorded, the higher the level of tape saturation that occurs. When tape saturation occurs the amount of harmonic distortion increases and the high frequency information is attenuated. This side effect has been used for years to add a certain sound quality to many recordings. In many cases the recording engineer will purposely overdrive many of the individually recorded tracks, such as vocals and individual instruments, to add this audible characteristic. Conversely, state of the art digital recording has a dynamic range of approximately 100 dB. Therefore, it is not desirable to overdrive digital recordings because the sound is not as pleasant to the ear.
Nevertheless, the benefits of digital recording outweigh those of analog and therefore digital is quickly becoming the most common recording format. There is, however, still a strong desire to provide the sonic artifacts associated with overdriven analog tape. Because of the high efficiency of digital recording components, digitally recorded material contains considerably more audible information, particularly high end information, than can be captured onto magnetic tape. But, when compared, the digital signal sounds much more harsh than the analog signal which has a much smoother high end.
As the industry has moved towards digital recording due to its higher level of control and performance, the absence of any product which provides exactly what analog tape saturation provided for the recording industry has caused people to begin using tube compressors, tube mic preamps and other products which are tube-based in an attempt to regain at least a small degree of the warmth that the analog tape machine provided. These tube-based products generate considerably higher distortion than their solid state counterparts, although not nearly as much as could be derived from the use of an analog tape machine. In addition, such products do not provide the bandwidth limitations which change dynamically, especially when transients occur. As analog tape is hit with a transient, such as a snare drum, saturation produces a loss of high frequency predominantly on the transient. During the decay of the instrument, the high frequency roll-off diminishes. Until now, the only method available to derive this effect was through the use of an analog tape machine.
It is, therefore, an object of this invention to provide an audio tape saturation simulator which yields the same auditory results when recording in the digital realm as would be accomplished if recording directly to analog tape. It is a further object of this invention to provide an audio tape saturation simulator which yields analog recording auditory results while allowing the recordist to maintain the efficiency, clarity and convenience of digital mediums. It is also an object of this invention to provide an audio tape saturation simulator which derives critical soft clipping distortion aspects by using either a vacuum tube, a solid state circuit, or a DSP algorithm modeled to provide similar performance results. Another object of this invention is to provide an audio tape saturation simulator which accepts digitally recorded signals, or can be used on individual instruments prior to recording, and transforms them into signals that sound as if they were recorded by traditional analog means. And it is an object of this invention to provide an audio tape saturation simulator which, as is the case when recording to analog tape, provides more saturation/distortion effect and greater reduction of the high frequency bandwidth of the signal as the signal is driven harder into the simulator.